Optical image-forming materials find many photographic applications, for example, for use as proof papers, printing-out papers, overlay films, etc. These are so-called free radical photographs in which imagewise exposed portions are visualized.
A particularly effective process in relation to the materials is a process of oxidizing various leuco dyes to corresponding colored dyes using a photo-oxidizing agent. However, since materials based on such a process are sensitive to light, color formation can take place even when there is exposure to ordinary room light, sunlight or white light, and even after formation of dye image by imagewise exposure. Thus, such optical image-recording materials are difficult to handle.
As techniques for preventing coloration of imagewise unexposed portions for the purpose of maintaining a once formed image, there have been proposed a technique of applying a solution of a reducing agent such as a free radical scavenger by spraying or impregnation to thereby maintain the originally recorded image, a technique of forming an image by UV light and fixing the material by activating a photo-reductive substance with visible light as described, for example, in JP-A-47-12879 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application"), and a technique of incorporating or coating a reducing, thermally fixing agent in or on a light-sensitive layer, and conducting thermal fixing after imagewise exposure as described in JP-B-43-29407 (the term "JP-B" as used herein refers to an "examined Japanese patent publication"). Of leuco dyes to be used in such optical image-forming materials, xanthene compounds having an anilino group in the 2-position, an alkyl group in the 3-position, and a substituted amino group in the 6-position are known as dyes showing a black hue in a colored state. However, such compounds have a defect in that they do not provide sufficient coloration density, and thus are not satisfactory.